1. Field of the Invention
The present invention relates generally to a planarization apparatus and method, and more particularly to a planarization apparatus and method for planarizing the reverse of a semiconductor wafer on which no chip is formed in a semiconductor wafer manufacturing process.
2. Description of Related Art
A planarization apparatus for grinding the reverse (one side) of a semiconductor wafer has chucks for holding the wafer by suction, a rough grinding wheel, a fine grinding wheel, a reverse cleaning unit, and the like. One chuck holds the obverse (the other side) of the wafer, and then the rough grinding wheel is pressed against the reverse of the wafer. The reverse of the wafer is roughly ground by rotating the chuck and the grinding wheel. The roughly-ground wafer is detached from the chuck and is held by another chuck for the fine grinding so that the wafer can be finely ground by the fine grinding wheel. The finely-ground wafer is transferred to the reverse cleaning unit so that the reverse of the wafer can be cleaned. That completes the grinding of the reverse of one wafer by the planarization apparatus.
The wafer whose reverse has already been ground is transferred from the planarization apparatus to an etching apparatus, which etches the wafer to remove a machining deteriorated layer formed at the reverse of the wafer.
If the wafer is ground into an extremely thin wafer close to a standardized article, the wafer is damaged (cracked or chipped) because of the machining deteriorated layer when the wafer is transferred from the planarization apparatus to the etching apparatus.
To address this problem, the conventional planarization apparatus grinds the wafer to such a thickness as not to damage the wafer during the transfer. With respect to the thickness of the wafer, the planarization apparatus roughly grinds the wafer with the thickness of 725 xcexcm sliced from an ingot to the thickness of 250 xcexcm, and finely grinds the wafer to the thickness of 200 xcexcm. The wafer is machined to the standardized thickness of 50 xcexcm at the etching step.
The conventional planarization apparatus, however, cannot grind the wafer close to the standardized thickness in order to prevent the wafer from being damaged during the transfer. For this reason, a machining allowance (150 xcexcm in the above example) is large at the etching step. Thus, it takes a long time to etch the wafer, and the throughput cannot be improved.
In view of the foregoing, it is an object of the present invention to provide a planarization apparatus and method which improve the throughput without damaging a workpiece.
The above object can be achieved by providing a planarization apparatus which comprises a holding means for holding a workpiece and a grinding means which has a grinding wheel for grinding the workpiece and grinds one side of the workpiece by the grinding wheel, the planarization apparatus comprising: a polishing means for polishing the one side of the workpiece, the polishing means comprising a rotating means for rotating a polishing head and a positioning mechanism for setting an interval between the polishing head and the workpiece.
The above object can be achieved by providing a planarization apparatus comprising: a holding means for holding a workpiece; a rough grinding means for roughly grinding the workpiece held by the holding means; a fine grinding means for finely grinding the workpiece roughly ground by the rough grinding means in the state wherein the holding means is holding the workpiece; a polishing means for polishing the workpiece finely ground by the fine grinding means in the state wherein the holding means is holding the workpiece; and a moving means for moving the holding means to a rough grinding position for the rough grinding means, a fine grinding position for the fine grinding means, and a polishing position for the polishing means.
The above object can be achieved by providing a planarization method using a planarization apparatus comprising: holding means for holding a workpiece; grinding means for grinding the workpiece held by the holding means; polishing means for polishing the workpiece ground by the grinding means; moving means for moving the holding means to a grinding position for the grinding means to grind the workpiece and to a polishing position for the polishing means to polish the workpiece; and wherein the polishing means polishes the workpiece by an amount more than an amount required for removing a machining deteriorated layer formed by the grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the grinding and removing the machining deteriorated layer, calculated by sextupling a standard deviation, and 20 xcexcm.
The above object can be achieved by providing a planarization method using a planarization apparatus comprising: holding means for holding a workpiece; rough grinding means for roughly grinding the workpiece held by the holding means; fine grinding means for finely grinding the workpiece roughly ground by the rough grinding means; polishing means for polishing the workpiece finely ground by the grinding means; moving means for moving the holding means to a rough grinding position for the rough grinding means, a fine grinding position for the fine grinding means and to a polishing position for the polishing means; wherein the fine grinding means finely grinds the workpiece by an amount more than an amount required for removing a machining deteriorated layer formed by the rough grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the rough grinding and removing the machining deteriorated layer, calculated by sextupling a standard deviation, and 150 xcexcm; and wherein the polishing means polishes the workpiece by an amount more than an amount required for removing a machining deteriorated layer formed by the fine grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the fine grinding and removing the machining deteriorated layer and calculated by sextupling a standard deviation, and 20 xcexcm.
According to the present invention, the planarization apparatus having the grinding means is provided with the polishing means, and this enables the grinding and polishing of the wafer in one apparatus. In the polishing method using the polishing means, the positioning mechanism positions the polishing head with respect to the workpiece, and the polishing head is pressed against the workpiece and is rotated by the rotating means. Consequently, the workpiece is polished. Since there is no necessity of transferring the workpiece from the planarization apparatus to the etching apparatus, the grinding means can grind the workpiece close to the standardized thickness. This reduces the time required for polishing the workpiece, and improves the throughput. The polishing removes the machining deteriorated layer formed by the grinding, and eliminates the necessity of etching in a post-treatment. This simplifies the entire structure of the workpiece manufacturing line, and reduces the size of the workpiece manufacturing line.
The workpiece may be polished in a constant pressure processing or in a constant cutting depth processing.
According to the present invention, the grinding means grinds the workpiece held by the holding means, and then, the polishing means polishes the workpiece after the moving means moves the holding means to the polishing position. More specifically, the workpiece held by the holding means is ground and polished, and it enables the accurate machining without damaging the workpiece. On the other hand, an apparatus, which transfers the workpiece from a holding means for grinding means to a holding means for a polishing means has such a problem that the workpiece may be damaged by an external force. Moreover, the accuracy of the holding face of the holding means changes every time the workpiece is transferred, and the accuracy affects the machining accuracy of the workpiece. Thus, the workpiece cannot be machined accurately. The present invention solves this problem.
According to the present invention, the planarization apparatus has cleaning means for cleaning a polishing pad and/or dressing means for dressing a surface of the polishing pad. If the polishing pad becomes dirty or loaded, the planarization apparatus cleans and dresses the polishing pad.
According to the present invention, the grinding means or the polishing means machines a machining deteriorated layer formed at one side of the workpiece ground in previous machining or machines the machining deteriorated layer and an unevenness of the thickness of the workpiece. It is therefore possible to acquire an accurate workpiece.
According to the present invention, the holding means is provided in a plural number, and the moving means sequentially moves the holding means from the grinding position to the polishing position so that the grinding and the polishing can be performed at the same time. This increases the availability compared with the case where one holding means grinds and polishes the workpiece.
According to the present invention, the holding means connects to a spindle and is moved by the moving means. This eliminates the necessity of separating the spindle from the holding means and connecting to the holding means to a spindle at the next moved position every time the holding means is moved.
According to the present invention, the holding means is detachably connected to a spindle, and when the holding means is moved, the holding means is separated from the spindle and only the holding means is moved by the moving means. This reduces the load on the moving means. Moreover, it is only necessary to provide the spindles suitable for each machining, and this reduces the manufacturing cost for the apparatus.
According to the present invention, the holding means is holding means for holding the workpiece by suction, holding means for freeze-holding the workpiece through ice film, or electrostatic holding means for holding the workpiece with static electricity. Thus, the workpiece can be held securely.
According to the present invention, the planarization apparatus further comprises a partitioning member for partitioning off a polishing position for the polishing means to polish the workpiece. Therefore, the grinding fluid and the grinding layer never reach the polishing position, and the polishing fluid used by the polishing means never reaches the grinding position. This prevents a trouble resulting from the mixture of the grinding and polishing fluids and chips. Particularly if the polishing means performs a chemical-mechanical polishing, the polishing fluid includes a chemical-mechanical agent. If the grinding fluid is mixed in this polishing fluid, the concentration of the chemical-mechanical agent is lowered and the machining time becomes longer. The use of the partition solves this problem.
According to the present invention, a planarization apparatus comprises rough grinding means, fine grinding means and polishing means so that the workpiece can be roughly ground, finely ground and polished automatically. Moreover the planarization apparatus has moving means for moving the holding means to a rough grinding position for the rough grinding means, a fine grinding position for the fine grinding means, and a polishing position for the polishing means. Consequently, the apparatus can work without lowering the rate of operation thereof even if single or plural rough grinding means, fine grinding means and polishing means are combined.
According to the present invention, the planarization apparatus with the rough grinding means, the fine grinding means and the polishing means is provided with etching means for etching the workpiece. Thus, one planarization apparatus can perform the machining sequence from the rough grinding to the etching. In this case, the etching means may etch the workpiece having been finely ground before the polishing, or may etch the workpiece having been polished. More specifically, the light etching aiming at cleaning the ground workpiece may be performed before the polishing. The etching may be performed after the polishing in order to eliminate impurities, heavy metal or dot defects harmful to element characteristics in the chips or to perform gettering.
According to the present invention, the planarization method uses the planarization apparatus comprises grinding means and polishing means. The polishing means polishes the workpiece by an amount more than an amount required for removing a machining deteriorated layer formed by the grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the grinding and removing the machining deteriorated layer, calculated by sextupling a standard deviation, and 20 xcexcm. This enables the desired machining without decreasing the availability of the apparatus.
According to the present invention, the planarization method uses the planarization apparatus comprises rough grinding means and fine grinding means as grinding means. The fine grinding means finely grinds by an amount more than an amount required for removing a machining deteriorated layer formed by the rough grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the rough grinding and removing the machining deteriorated layer, calculated by sextupling a standard deviation, and 150 xcexcm. The polishing means polishes the workpiece by an amount more than an amount required for removing a machining deteriorated layer formed by the fine grinding, calculated by doubling a standard deviation, and less than a larger value between an amount required for correcting an unevenness of a thickness during the fine grinding and removing the machining deteriorated layer, calculated by sextupling a standard deviation, and 20 xcexcm.
According to the present invention, the planarization apparatus has a sensor for measuring the thickness of the workpiece prior to machining or during machining, and the planarization apparatus controls the amount of material to be ground or polished in accordance with a measured value.